1. Field of the Invention
This invention relates to molded gaskets having compression limiter members and internal wire stiffener members.
2. Description of Prior Developments
Gaskets formed of resilient elastomeric materials are commonly used to seal the interface between various members designed to cooperatively contain or transport fluids. Such gaskets are required to prevent the escape of fluid along a nominally sealed joint.
Quite often such gaskets are formed with through holes located at spaced points around the gasket periphery. These holes accommodate bolts or studs that are used to compress the gasket material between two fluid containment members. Compression of the gasket material deforms it so as to fill minor cracks or crevices that could provide escape routes for the sealed fluid.
However, if the gasket material is overly compressed at localized points, it can extrude out of the sealed joint and stretch to the point of rupture. Moreover, uneven compression of the gasket material surrounding different bolts or studs can warp the gasket to produce leakage paths where the compression is low.
In order to control or limit the compression of elastomeric gaskets, it is a practice to embed rigid members in the gasket, particularly at those points where the fastener bolts or studs extend through the gasket material. Each bolt or stud typically extends through a hole formed within one of the rigid members. The rigidity of these members ensures that the gasket material will not be overly compressed due to overtorquing the studs or bolts. Such members are sometimes referred to as compression limiter rings.
Gaskets formed of elastomeric materials tend to be especially flexible when formed to a durometer suitable for optimum sealing action. Such flexibility or limpness is a disadvantage when the gasket is being installed. A limp rope-like gasket loses its shape so that it becomes difficult to install.
In order to stiffen the gasket so that it maintains a prescribed shape for installation purposes, it is a practice to employ a flexible metal stiffener sheet or wire within the molded gasket material. In some cases, the preformed stiffener is deployed as an insert in the mold used to form the gasket, such that the elastomer is molded around the stiffener.
U.S. Pat. No. 3,191,950 to Hiltner shows a gasket having a number of compression limiter rings disposed at preselected points around the gasket periphery. The axial thickness of each ring is less than the maximum thickness of the gasket, as defined by sealing beads that project from the major faces of the gasket.
The end faces of the rings act as compression limiters when bolts or studs are torqued to connect the members that are to be sealed by the gasket. The rings are formed integrally with an internal stiffener sheet which is coextensive with the face area of the gasket. Two flat annular washers are welded to opposite faces of the stiffener sheet to form a three-piece laminated ring structure.
U.S. Pat. No. 4,535,996 to Cardis et al. shows a molded elastomeric gasket having a stiffener core sheet formed with circular holes. A flanged ring is held in each circular hole by staking areas of the ring side wall against one face of the core sheet. The end faces of the flanged rings are exposed so that the rings can act to limit the compression of the elastomeric gasket material.
U.S. Pat. No. 4,655,463 to Inciong shows a deformable gasket having a metallic stiffener sheet and an array of compression limiter rings spaced around the sheet periphery. Each ring includes two mating ring elements arrangeable on opposite faces of the stiffener sheet, so that one ring element extends through the sheet plane as a press fit in the other element.
Gaskets of the type disclosed in the above-mentioned patents are somewhat expensive, due in part to the cost of the metallic stiffener sheets. Such sheets have to be stamped with mounting holes for receiving the compression limiter rings. Relatively expensive progressive dies are required to form the sheets to the necessary precision. Also, the scrap losses are relatively great because the sheet area circumscribed by the annular sheet must be discarded. Only a small fraction of the total sheet area is used for stiffening purposes in the molded gasket.